Chill. Eating a bit of dirt (you said something like a tea/tablespoon, right?) won't hurt him, and it's better than eating poop.

*takes old granny voice* Ya know, if he was in nature, he'd be eating off the ground, and eating dirty stuff, and innards of animals that eat grass and by procuration, dirt, and he'd eat a whole lot more dirt than what he gets now. And he'd still be fine. *ufolds from hunchback position, lets go of cane*